Reports earlier said a 17-year-old girl died on the way to hospital and two people were injured in the shooting, including a 17-year-old boy, who was in critical but stable condition, and an adult employee who was treated and released at the scene.

No arrest has been made and police are in possession of the weapon used in the incident, Birmingham police Chief Orlando Wilson told a news conference.

"At this particular time, we consider it accidental until the investigation takes us elsewhere," Wilson said according to AL.com, an Alabama news website.

"We have a lot of unanswered questions. There are so many unknowns at this time."

The Alabama school has working metal detectors and would be open on Thursday with heightened security and a crisis team on hand, Lisa Herring, superintendent of Birmingham City Schools, told reporters.

The student who died was a graduating senior who would soon be 18 years old, had been accepted to college and wanted to become a nurse, Birmingham Mayor Randall Woodfin told reporters.

"Our hearts are heavy," Woodfin said.

Tonight, let us wrap our arms around the Huffman community. Today, we lost a 17 year old student. A daughter, a niece, a grandchild. An incredible person that was aspiring to be a nurse. Our hearts are heavy, and our prayers are with the Huffman community.